1. Field of the Invention
The invention relates to a turbocharger in which a variable nozzle mechanism that makes variable the flow velocity of exhaust gas blown onto a turbine wheel by causing a variable nozzle to operate in an opening/closing manner is incorporated.
2. Description of the Related Art
As a turbocharger that is mounted on an engine, there is a turbocharger in which a variable nozzle mechanism that makes variable the flow velocity of exhaust gas blown onto a turbine wheel by causing a variable nozzle to operate in an opening/closing manner is incorporated.
For example, in a turbocharger described in Japanese Patent Application Publication No. 2009-144545 (JP-2009-144545 A), as shown in FIG. 5, a turbine shaft 71 is rotatably supported by a bearing housing 72. A turbine housing 73 is arranged on one side of the bearing housing 72 (on the left side in FIG. 5) in a direction along an axis L1 of the turbine shaft 71. The turbine housing 73 has a turbine chamber 74 at a central portion thereof, and has a convolute scroll passage 75 around the turbine chamber 74. A turbine wheel 76 that rotates in the aforementioned turbine chamber 74 is provided on the turbine shaft 71. In addition, in this turbocharger 70, an exhaust gas E that has flowed along the scroll passage 75 after being discharged from an engine is blown onto the turbine wheel 76, and the turbine wheel 76 is rotationally driven. As a result of this, a compressor wheel (not shown) that is coaxial with the turbine wheel 76 rotates integrally with the turbine wheel 76, so that the engine is supercharged (intake air is compressed and delivered to the engine).
An annular support member 79 having a plurality of through-holes 78 that penetrate therethrough in the direction along the aforementioned axis L1 (a lateral direction in FIG. 5) is arranged in an annular communication passage 77 between the aforementioned scroll passage 75 and the aforementioned turbine chamber 74. Shafts 81 are turnably inserted through the through-holes 78 respectively, and variable nozzles 82 are fixed to the shafts 81 respectively. In addition, each of the variable nozzles 82 is operated in an opening/closing manner by being turned integrally with a corresponding one of the shafts 81. The flow velocity of the exhaust gas E that is blown onto the turbine wheel 76 is changed, the rotational speed of the turbocharger 70 is changed, and the boost pressure (the intake pressure) of the engine is adjusted.
An annular sealing member 83 is so arranged as to surround the turbine wheel 76, in a gap G between the support member 79 and the turbine housing 73, in the direction along the aforementioned axis L1. The aforementioned gap G is sealed upstream of the aforementioned through-holes 78 with respect to the flow of exhaust gas by this sealing member 83. Thus, the exhaust gas E in the scroll passage 75 is restrained from leaking out through the gap G.
However, in the turbocharger 70 described in the aforementioned Japanese Patent Application Publication No. 2009-144545 (JP-2009-144545 A), when the exhaust gas E leaks out to the gap G through between the through-holes 78 and the shafts 81 as indicated by an arrow in FIG. 5 in the process of passing through between adjacent ones of the variable nozzles 82 from the scroll passage 75, the exhaust gas E flows along the gap G downstream with respect to the flow of exhaust gas. In addition, this exhaust gas E is discharged from an outlet 84, which is located at a downstream end of the gap G downstream of the turbine wheel 76 with respect to the flow of exhaust gas, without passing the turbine wheel 76. Thus, the amount of the exhaust gas E that is blown onto the turbine wheel 76 decreases by an amount of the discharged exhaust gas. As a result, the rotational speed of the turbocharger 70 may become low, and the boost pressure of the engine may decrease.